EP0301952B1 - Compound oxide superconducting material and method for preparing the same - Google Patents
Compound oxide superconducting material and method for preparing the same Download PDFInfo
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- EP0301952B1 EP0301952B1 EP88401931A EP88401931A EP0301952B1 EP 0301952 B1 EP0301952 B1 EP 0301952B1 EP 88401931 A EP88401931 A EP 88401931A EP 88401931 A EP88401931 A EP 88401931A EP 0301952 B1 EP0301952 B1 EP 0301952B1
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- superconducting material
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- 239000000463 material Substances 0.000 title claims description 47
- 150000001875 compounds Chemical class 0.000 title claims description 30
- 238000000034 method Methods 0.000 title claims description 29
- 239000000843 powder Substances 0.000 claims description 58
- 238000005245 sintering Methods 0.000 claims description 31
- 229910052788 barium Inorganic materials 0.000 claims description 16
- 239000013078 crystal Substances 0.000 claims description 16
- 239000000203 mixture Substances 0.000 claims description 15
- 239000010409 thin film Substances 0.000 claims description 12
- 229910052791 calcium Inorganic materials 0.000 claims description 10
- 238000010438 heat treatment Methods 0.000 claims description 10
- 239000002245 particle Substances 0.000 claims description 10
- 238000010298 pulverizing process Methods 0.000 claims description 8
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 7
- 229910052746 lanthanum Inorganic materials 0.000 claims description 7
- 239000001301 oxygen Substances 0.000 claims description 7
- 229910052760 oxygen Inorganic materials 0.000 claims description 7
- 229910052727 yttrium Inorganic materials 0.000 claims description 7
- 229910052802 copper Inorganic materials 0.000 claims description 6
- 229910052716 thallium Inorganic materials 0.000 claims description 6
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 claims description 5
- 229910001882 dioxygen Inorganic materials 0.000 claims description 5
- 239000011230 binding agent Substances 0.000 claims description 3
- 238000001816 cooling Methods 0.000 claims description 3
- 230000008018 melting Effects 0.000 claims description 3
- 238000002844 melting Methods 0.000 claims description 3
- 238000005240 physical vapour deposition Methods 0.000 claims description 3
- 239000000758 substrate Substances 0.000 claims description 3
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 claims description 2
- 229910002651 NO3 Inorganic materials 0.000 claims 1
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 claims 1
- MUBZPKHOEPUJKR-UHFFFAOYSA-N Oxalic acid Chemical compound OC(=O)C(O)=O MUBZPKHOEPUJKR-UHFFFAOYSA-N 0.000 claims 1
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 claims 1
- 239000002887 superconductor Substances 0.000 description 10
- 239000010408 film Substances 0.000 description 3
- 239000001307 helium Substances 0.000 description 3
- 229910052734 helium Inorganic materials 0.000 description 3
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 description 3
- 238000010248 power generation Methods 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 description 2
- 229910002370 SrTiO3 Inorganic materials 0.000 description 2
- AYJRCSIUFZENHW-UHFFFAOYSA-L barium carbonate Chemical compound [Ba+2].[O-]C([O-])=O AYJRCSIUFZENHW-UHFFFAOYSA-L 0.000 description 2
- 238000009835 boiling Methods 0.000 description 2
- 239000010419 fine particle Substances 0.000 description 2
- 230000004927 fusion Effects 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 238000004544 sputter deposition Methods 0.000 description 2
- 229910021521 yttrium barium copper oxide Inorganic materials 0.000 description 2
- IOMKFXWXDFZXQH-UHFFFAOYSA-N (6-oxo-7,8,9,10-tetrahydrobenzo[c]chromen-3-yl) 3-chloro-4-[3-[(2-methylpropan-2-yl)oxycarbonylamino]propanoyloxy]benzoate Chemical compound C1=C(Cl)C(OC(=O)CCNC(=O)OC(C)(C)C)=CC=C1C(=O)OC1=CC=C(C2=C(CCCC2)C(=O)O2)C2=C1 IOMKFXWXDFZXQH-UHFFFAOYSA-N 0.000 description 1
- 229910017569 La2(CO3)3 Inorganic materials 0.000 description 1
- 229910000750 Niobium-germanium Inorganic materials 0.000 description 1
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 1
- 229910009440 Y2(CO3)3 Inorganic materials 0.000 description 1
- 229910003098 YBa2Cu3O7−x Inorganic materials 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 229910000019 calcium carbonate Inorganic materials 0.000 description 1
- 235000010216 calcium carbonate Nutrition 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 230000002950 deficient Effects 0.000 description 1
- 238000007606 doctor blade method Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000001125 extrusion Methods 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 238000007733 ion plating Methods 0.000 description 1
- 230000002045 lasting effect Effects 0.000 description 1
- 238000005339 levitation Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 239000000523 sample Substances 0.000 description 1
- 229910052594 sapphire Inorganic materials 0.000 description 1
- 239000010980 sapphire Substances 0.000 description 1
- 229910052709 silver Inorganic materials 0.000 description 1
- 239000004332 silver Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 229910000012 thallium(I) carbonate Inorganic materials 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- 238000001771 vacuum deposition Methods 0.000 description 1
- 238000009834 vaporization Methods 0.000 description 1
- 230000008016 vaporization Effects 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
- C04B35/45—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on copper oxide or solid solutions thereof with other oxides
- C04B35/4512—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on copper oxide or solid solutions thereof with other oxides containing thallium oxide
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N60/00—Superconducting devices
- H10N60/01—Manufacture or treatment
- H10N60/0268—Manufacture or treatment of devices comprising copper oxide
- H10N60/0296—Processes for depositing or forming copper oxide superconductor layers
- H10N60/0408—Processes for depositing or forming copper oxide superconductor layers by sputtering
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N60/00—Superconducting devices
- H10N60/80—Constructional details
- H10N60/85—Superconducting active materials
- H10N60/855—Ceramic superconductors
- H10N60/857—Ceramic superconductors comprising copper oxide
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S505/00—Superconductor technology: apparatus, material, process
- Y10S505/775—High tc, above 30 k, superconducting material
- Y10S505/776—Containing transition metal oxide with rare earth or alkaline earth
- Y10S505/779—Other rare earth, i.e. Sc,Y,Ce,Pr,Nd,Pm,Sm,Eu,Gd,Tb,Dy,Ho,Er,Tm,Yb,Lu and alkaline earth, i.e. Ca,Sr,Ba,Ra
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S505/00—Superconductor technology: apparatus, material, process
- Y10S505/775—High tc, above 30 k, superconducting material
- Y10S505/776—Containing transition metal oxide with rare earth or alkaline earth
- Y10S505/783—Thallium-, e.g. Tl2CaBaCu308
Definitions
- the present invention relates to a superconducting material and a method for preparing the same. More particularly, it relates to a novel superconducting material composed of compound oxide having a higher critical temperature and a method for preparing the same.
- the superconductivity can be utilized in the field of power electric applications such as MHD power generation, fusion power generation, power transmission, electric power reservation or the like; in the field of transportation for example magnetic levitation trains, magnetically propelling ships or the like; in the medical field such as high-energy beam radiation unit; in the field of science such as NMR or high-energy physics; a high sensitive sensors or detectors for sensing very weak magnetic field, microwave, radiant ray or the like, or in the field of fusion power generation.
- the superconducting materials can be used in the field of electronics, for example, as a device using the Josephson device which is expected to be a high-speed and low-power consuming switching device.
- the sintering temperature is one of the critical factors in the process for producing the superconduting compound oxide, so that the sintering temperature is controlled and adjusted to a temperature at which the sintering proceed in a solid reaction without substantial fusing of the material powder and excessive crystal growth is not occur in the resulting sintered compound oxide.
- the sintering temperature should not exceed the lowest melting point of any component in the material powder such as the powder mixture, the compound powder or the preliminary sintered powder. To the contrary, satisfactory sintering can not be effected if the sintering temperature is too low. Therefore the sintering must be carried out a temperature which is higher than 700 °C. Duration of sintering operation is generally for 1 hour to 50 hours in actual practice, although longer sintering time is preferable.
- the sintered compound oxide is further heat-treated in order to homogenize the crystal structure. This heat-treatment improve the critical temperature and reduce remarkably the discrepancy between the terminal temperature of phase change where perfect zero resistance is observed and the critical temperature.
- This heat-treatment is preferably carried out in an oxygen containing atmosphere at a temperature of 500 to 900 °C.
- the crystal structure of sintered compound oxide is stabilized and the oxygen deficient perovskite structure which is desired for realizing the superconductivity is obtained, resulting in that the lower critical temperature where perfect zero resistance is observed become much higher and a lasting and stable superconductor is assured.
- the temperature of heat-treatment is not higher than 500 °C the abovementioned effect is not obtained or it takes longer time before realization of the objective crystal structure. To the contrary, if the temperature of heat-treatment exceed 900 °C, the abovementioned perovskite type crystal structure is lost.
- the superconducting material according to the present invention can be used in a form of a sintered mass or article as it is and is also used in a form of a powder which is prepared by pulverizing the sintered mass.
- This powder-formed superconducting compound oxide can be used for producing a superconducting wire or the like.
- the superconducting compound oxide powder according to the present invention is compacted in a metallic pipe which is then drawn into a fine wire or is mixed with suitable binder such as polybutylbutylal (PVB) to prepare a paste which can be molded into a desired configuration or which is coated or applied in a desired pattern. The resulting wire and the paste molded or coated are then sintered finally.
- PVB polybutylbutylal
- the superconducting compound oxide according to the present invention is used in the form of a paste, it is preferable to heat the coated or molded paste at 400 to 700 °C in air before the final sintering operation in order to remove the binder previously.
- a thickness of the paste to be molded is adjusted to less than 0.6 mm, because a pre-form molded with the paste by a doctor blade coating technique or extrusion technique shrink during the final sintering stage so that the dimension of the final product becomes smaller. Therefore, when the paste is shaped into a form of a thick film or a tape or wire, their thickness or diameter of paste coated or molded is preferably controlled to less than 0.6 mm and 1.2 mm.
- the vapor source may be a block prepared by sintering the material powder such as (i) powders of metal elements of Ba, Cu, ⁇ , ⁇ and ⁇ (elements ⁇ , ⁇ and ⁇ have the same definition as above) as they are, (ii) a powder mixture of compounds of these elements or (iii) their combination.
- the vapor source may be a powder which is obtained by pulverizing the sintered block. The proportion or atomic ratio of the elements in the vapor source is selected in such manner that the desired atomic ratio of the elements are realized in the deposited thin film in consideration of vaporization rate or sputtering rate or the like.
- the abovementioned heat-treatment of the deposited thin film is very effective.
- the heat-treatment is carried out at a temperature of 500 to 900 °C for more than 1 hour in oxygen containing atmosphere in which the partial pressure of oxygen is adjusted to 0,135 to 135.102 Pa (10 ⁇ 3 to 102 Torr). After the heat-treatment, the resulting thin film is cooled slowly at a cooling rate of less than 10 °C/min.
- the superconducting material according to the present invention show a very high critical temperature comparing to the conventional materials. This might come from their characteristic feature of the composition and their uniform and fine crystal structure which is assured by the present process.
- Powders of commercially available CuO and carbonate powders of Ba, Ca, La, Y and Tl namely BaCO3, CaCO3, La2(CO3)3, Y2(CO3)3, Dy2(CO3)3, Tl2CO3 are mixed in such an atomic ratio that satisfies the following general formula: (Ba, Ca) x ( ⁇ , Dy) 1-x Tl y Cu 1-y in which ⁇ represents La or Y, the value of x and y are shown in Table 1, and the proportion (%) of Ca with respect to Ba and the proportion (%) of Dy with respect to ⁇ are also shown in the Table 1.
- the respective powder mixtures are pulverized in a ball mill to be reduced to an average particle size of 4 ⁇ m and then sintered at 750 °C for 15 hours.
- the resulting sintered mass or cake is pulverized again.
- the steps of sintering and pulverization are repeated two times under the same condition as above.
- the finally obtained powder of less than 4 ⁇ m is charged in a rubber mold and compressed hydrostatically under a pressure of 1.5 ton/cm2 to obtain tablets of 4 x 10 x 30 mm.
- the tablets are sintered at 950 °C for 8 hours in air.
- Measurement of an upper critical temperature Tc and a lower critical temperature Tcf is effected by a conventional four probe method. Temperature is measured by a calibrated Au(Fe)-Ag thermocouple.
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Ceramic Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Structural Engineering (AREA)
- Organic Chemistry (AREA)
- Compositions Of Oxide Ceramics (AREA)
- Inorganic Compounds Of Heavy Metals (AREA)
Description
- The present invention relates to a superconducting material and a method for preparing the same. More particularly, it relates to a novel superconducting material composed of compound oxide having a higher critical temperature and a method for preparing the same.
- Under the phenomenon of superconductivity, the perfect diamagnetism is observed and no difference in potential is observed for all that an electric current of a constant finite value is observed internally.
- The superconductivity can be utilized in the field of power electric applications such as MHD power generation, fusion power generation, power transmission, electric power reservation or the like; in the field of transportation for example magnetic levitation trains, magnetically propelling ships or the like; in the medical field such as high-energy beam radiation unit; in the field of science such as NMR or high-energy physics; a high sensitive sensors or detectors for sensing very weak magnetic field, microwave, radiant ray or the like, or in the field of fusion power generation. In addition to the abovementioned power electric applications, the superconducting materials can be used in the field of electronics, for example, as a device using the Josephson device which is expected to be a high-speed and low-power consuming switching device.
- The phenomenon of superconductivity, however, is observed only at very low cryogenic temperatures. In fact, a relatively lower temperature of 23.2 K which was the critical temperature (Tc) of a superconductor composed of Nb₃Ge have been the top record of the critical temperature among known superconducting materials.
- This means that liquidized helium (boiling point of 4.2K) is only one cryogen which can realize such very low temperature of Tc. However, helium is not only a limited costly resource but also require a large-scaled system for liquefaction. Therefore, there had been a strong demand for another superconducting materials having higher Tc. But no material which exceeded the abovementioned Tc had been found for all studies for the past ten years.
- Possibility of existence of a new type of superconducting materials having much higher Tc was revealed by Bednorz and Müller who discovered a new oxide type superconductor in 1986 [Z. Phys. B64 (1986) 189]. It was also reported in the news paper that C. W. Chu et al. discovered in the United States of America another superconducting material so called YBCO type represented by YBa₂Cu₃O7-x having the critical temperature of about 90 K in February 1987. And hence, possibility of existence of high-temperature superconductors have burst on the scene.
- It had been known that certain ceramics material of compound oxides exhibit the property of superconductivity. For example, U. S. patent No. 3,932,315 discloses Ba-Pb-Bi type compound oxide which shows superconductivity and Japanese patent laid-open No. 60-173,885 discloses that Ba-Bi type compound oxides also shown superconductivity. These superconductors, however, possess rather lower transition temperatures of about 10 K and hence usage of liquidized helium (boiling point of 4.2 K) as cryogen had been indispensable to realize superconductivity. Therefore, the abovementioned new type compound oxides in which superconductivity is realized in liquid nitrogen which is a relatively cheap cryogen will accelerate actual usage of superconductors.
- Physical Review Letters, Vol. 58, n° 18, 4th May 1987, pp. 1888-1890, discloses a variation of YBCO oxide superconductor having Tc lower than 100K, but is silent to metal element of IIIb group of the present invention.
- An object of the present invention is to provide a new system of compound oxide which possess a higher critical temperature and a method for preparing the same.
- A superconducting material according to the present invention is composed of a compound oxide represented by the general formula:
(Ba, Ca)x(α, Dy)1-xTlyCu1-xO3-z
in which
an atomic ratio of Ca to Ba being selected in a range between 1 % and 90 %.
"α" represents Y or La,
an atomic ratio of Dy to α is selected in a range between 1 % and 90 %.
x, y, and z are numbers each satisfies ranges of 0 < x < 1,0 < y <1, and 0 ≦ z < 1 respectively, and
the expression of (Ba, Ca) and (α, Dy) mean that the respective elements position predetermined sites in a crystal in a predetermined proportion. - A process for producing a superconducting material according to the present invention comprise preparing a material powder, compacting the material powder and then subjecting the resulting compact to final sintering, and said process is characterized in that said material powder is a member selected from a
group consisting of: - (A) a powder mixture composed of powders selected from a group comprising
- (i) powders of elements Ba, Cu, α, Dy, Ca and Tl and
- (ii) powders of compounds each containing at least one of said elements Ba, Cu, α, Dy, Ca and Tl,
- (B) a sintered powder obtained by sintering preliminarily the powder mixture (A) and then pulverizing a sintered mass and
- (C) a powder mixture of said powder mixture (A) and said sintered powder (B),
- The sintered compact obtained by the abovementioned process is composed of so-called quasi-perovskite type compound oxide which is represented by the general formula:
(Ba, Ca)x(α, Dy)1-xTlyCu1-yO3-z
in which
an atomic ratio of Ca to Ba being selected in a range between 1 % and 90 %,
"α" represents Y or La,
an atomic ratio of Dy to α is selected in a range between 1 % and 90 %,
x, y and z are numbers each satisfies ranges of 0 < x < 1, 0 < y <1, and 0 ≦ z < 1 respectively, and
the expression of (Ba, Ca) and (α, Dy) mean that the respective elements position predetermined sites in a crystal in a predetermined proportion. - The atomic ratio of Ca to Ba can be selected in a range between 1 % and 90 % but a preferred result is obtained in a range between 1 % and 50 %. Still more, there is such tendency that preferable properties as superconductors are obtained when the value of x is selected in a range of 0.3 ≦ x ≦ 0.4.
- The essence of the present invention resides in that the compound oxide is composed of the abovementioned specified elements and oxygen. This is a unique point of the present invention, comparing to abovementioned known new type superconductors composed of four elements. Namely, the compound oxide according to the present invention, two pairs of elements each pair of which belongs to the same group of the periodic table. It is thought that an advantageous result of the present invention is obtained when each of these elements occupies a predetermined site in the crystal in a predetermined proportion.
- In order to obtain a sintered compound oxide possessing superior superconducting properties, it is indispensable to control the following factors:
- (i) particle size of the material powder,
- (ii) temperature during the preliminary sintering operation,
- (iii) particle size of the preliminary sintered and pulverized powder, and
- (iv) temperature during the final sintering operation.
- In fact, if an average particle size of the material powder exceed 10 µm, a fine particle which is satisfactory in uniformity can not be obtained easily even after such material powder is subjected to the preliminary sintering operation. Therefore, the average particle size of the material powder is preferably less than 10 µm.
- In case that a sintered powder (B) which is prepared by preliminary sintering of the powder mixture (A) is used as the material powder, the preliminary sintering is preferably carried out at a temperature which is higher than 700 °C but is not higher than the lowest melting point of any compound which is contained in the powder mixture (A) for a duration of from 1 to 50 hours and preferably in an atmosphere containing oxygen gas of 0.135 to 135.10² Pa (10⁻³ to 10² Torr). It is also preferable that, after the preliminary sintering complete, the resulting sintered mass is cooled at a cooling rate which is not slower than 1 °C/min but not higher than 1,000 °C/min. A particle size of the pulverized powder obtained from the preliminary sintered mass influence directly upon a particle size of a crystal which is obtained after the final sintering operation, so that the preliminary sintered mass is preferably pulverized to powder having an average particle size of less than 5 µm. Such fine particles increase the area of grain boundaries which is one of critical factors for realizing the superior superconductor which is particularly improved in the critical temperature of superconductivity. Pulverization or reduction of the preliminary sintered mass to less than 1 µm is not only economical or practicable but also increase possibility of contamination of the material powder. Therefore, the average particle size of the preliminary sintered powder is preferably adjusted to a range between 1 µm and 5 µm.
- A series of operations of preliminary sintering, pulverization and compacting is preferably repeated for several times to homogenize the material powder.
- The sintering temperature is one of the critical factors in the process for producing the superconduting compound oxide, so that the sintering temperature is controlled and adjusted to a temperature at which the sintering proceed in a solid reaction without substantial fusing of the material powder and excessive crystal growth is not occur in the resulting sintered compound oxide. In fact, the sintering temperature should not exceed the lowest melting point of any component in the material powder such as the powder mixture, the compound powder or the preliminary sintered powder. To the contrary, satisfactory sintering can not be effected if the sintering temperature is too low. Therefore the sintering must be carried out a temperature which is higher than 700 °C. Duration of sintering operation is generally for 1 hour to 50 hours in actual practice, although longer sintering time is preferable.
- The abovementioned preliminary sintering operation should be also controlled precisely in the same manner as above because of the same reason.
- According to a preferred embodiment, the sintered compound oxide is further heat-treated in order to homogenize the crystal structure. This heat-treatment improve the critical temperature and reduce remarkably the discrepancy between the terminal temperature of phase change where perfect zero resistance is observed and the critical temperature.
- This heat-treatment is preferably carried out in an oxygen containing atmosphere at a temperature of 500 to 900 °C. Under this condition of heat-treatment, the crystal structure of sintered compound oxide is stabilized and the oxygen deficient perovskite structure which is desired for realizing the superconductivity is obtained, resulting in that the lower critical temperature where perfect zero resistance is observed become much higher and a lasting and stable superconductor is assured. If the temperature of heat-treatment is not higher than 500 °C the abovementioned effect is not obtained or it takes longer time before realization of the objective crystal structure. To the contrary, if the temperature of heat-treatment exceed 900 °C, the abovementioned perovskite type crystal structure is lost.
- The superconducting material according to the present invention can be used in a form of a sintered mass or article as it is and is also used in a form of a powder which is prepared by pulverizing the sintered mass. This powder-formed superconducting compound oxide can be used for producing a superconducting wire or the like. For example, the superconducting compound oxide powder according to the present invention is compacted in a metallic pipe which is then drawn into a fine wire or is mixed with suitable binder such as polybutylbutylal (PVB) to prepare a paste which can be molded into a desired configuration or which is coated or applied in a desired pattern. The resulting wire and the paste molded or coated are then sintered finally.
- When the superconducting compound oxide according to the present invention is used in the form of a paste, it is preferable to heat the coated or molded paste at 400 to 700 °C in air before the final sintering operation in order to remove the binder previously.
- When a self-supporting article is molded with the paste, it is preferable to select a thickness of the paste to be molded to less than 1.2 mm and when a thick film is coated on a support, the thickness of a layer of paste to be coated on a support is adjusted to less than 0.6 mm, because a pre-form molded with the paste by a doctor blade coating technique or extrusion technique shrink during the final sintering stage so that the dimension of the final product becomes smaller. Therefore, when the paste is shaped into a form of a thick film or a tape or wire, their thickness or diameter of paste coated or molded is preferably controlled to less than 0.6 mm and 1.2 mm.
- The superconducting material according to the present invention can be formed into a thin film by the conventional physical vapor deposition (PVD) technique such as vacuum deposition, sputtering, ion-plating or molecular beam epitaxial growth technique in the presence of oxygen gas. In this case, the abovementioned sintered mass or block is used as a vapor source or target which is evaporated in a vacuum chamber to produce a thin film deposited on a substrate. Namely, the vapor source may be a block prepared by sintering the material powder such as (i) powders of metal elements of Ba, Cu, α, β and ε (elements α, β and ε have the same definition as above) as they are, (ii) a powder mixture of compounds of these elements or (iii) their combination. The vapor source may be a powder which is obtained by pulverizing the sintered block. The proportion or atomic ratio of the elements in the vapor source is selected in such manner that the desired atomic ratio of the elements are realized in the deposited thin film in consideration of vaporization rate or sputtering rate or the like. The oxygen pressure in the vacuum chamber should be controlled so that the partial pressure of oxygen gas is adjusted to a range between 1-35. 10⁻⁴ and 1.35 Pa (10⁻⁶ and 10⁻² Torr). The substrates on which the thin film are deposited are preferably those that have similar crystal structure or lattice constant and may be a single crystal of MgO, sapphire or SrTiO₃. Desirably, the superconducting thin film is deposited on a {001} plane or {110} plane of a single crystal of MgO or SrTiO₃ to improve the critical current density (Jc) owing to ordering of crystal to c-axis.
- In this case of thin film also, the abovementioned heat-treatment of the deposited thin film is very effective. The heat-treatment is carried out at a temperature of 500 to 900 °C for more than 1 hour in oxygen containing atmosphere in which the partial pressure of oxygen is adjusted to 0,135 to 135.10² Pa (10⁻³ to 10² Torr). After the heat-treatment, the resulting thin film is cooled slowly at a cooling rate of less than 10 °C/min.
- The superconducting material according to the present invention show a very high critical temperature comparing to the conventional materials. This might come from their characteristic feature of the composition and their uniform and fine crystal structure which is assured by the present process.
- The novel superconducting materials according to the present invention have improved stability and a high critical temperature, so that they can realized superconductivity by means of relatively cheaper cryogen in a small liquefication system and hence they can be utilized advantageously in applications of superconducting wire, rod, parts such as magnets, thick film or thin film devices, such as Matisoo switching elements (Appl. Phys. Lett.,(9), p. 166-168) or Josephson device, Anacker memory device (IEEE trans. Magn. vol. MAG-5, p.968-975), a variety of sensors or Superconducting Quantum Interference Device (SQUID).
- Now, embodiments of the process according to the present invention will be described by Examples, but the scope of the present invention should not be limited thereto.
- Powders of commercially available CuO and carbonate powders of Ba, Ca, La, Y and Tl, namely BaCO₃, CaCO₃, La₂(CO₃)₃, Y₂(CO₃)₃, Dy₂(CO₃)₃, Tl₂CO₃ are mixed in such an atomic ratio that satisfies the following general formula:
(Ba, Ca)x(α, Dy)1-xTlyCu1-y
in which
α represents La or Y, the value of x and y are shown in Table 1, and the proportion (%) of Ca with respect to Ba and the proportion (%) of Dy with respect to α are also shown in the Table 1. - The respective powder mixtures are pulverized in a ball mill to be reduced to an average particle size of 4 µm and then sintered at 750 °C for 15 hours. The resulting sintered mass or cake is pulverized again. The steps of sintering and pulverization are repeated two times under the same condition as above. The finally obtained powder of less than 4 µm is charged in a rubber mold and compressed hydrostatically under a pressure of 1.5 ton/cm² to obtain tablets of 4 x 10 x 30 mm. The tablets are sintered at 950 °C for 8 hours in air.
- Resistance is measured on the tablets on which electrodes are secured with silver electroconductive paste to determine the critical temperature.
- Measurement of an upper critical temperature Tc and a lower critical temperature Tcf is effected by a conventional four probe method. Temperature is measured by a calibrated Au(Fe)-Ag thermocouple.
-
in which, "α" represents Y or La,
wherein, an atomic ratio of (Ba, Ca) : (α, Dy) : Tl : Cu in said material powder satisfies a ratio of x : (1-x) : y : (1-y), in which an atomic ratio of Ca to Ba is selected in a range between 1 % and 90 %, an atomic ratio of Dy to α is selected in a range between 1 % and 90 %, x and y are numbers each satisfies ranges of 0 < x < 1 and 0 < y < 1 respectively.
Claims (19)
- A superconducting material comprising a compound oxide represented by the general formula:
(Ba, Ca,)x(α, Dy)1-xTlyCu1-yO3-z
in which
an atomic ratio of Ca to Ba being selected in a range between 1 % and 90 %,
"α" represents Y or La,
an atomic ratio of Dy to α is selected in a range between 1 % and 90 %,
x, y and z are numbers each satisfies ranges of 0 < x < 1, 0 < y <1, and 0 ≦ z < 1 respectively, and
the expression of (Ba, Ca) and (α, Dy) mean that the respective elements position predetermined sites in a crystal in a predetermined proportion. - The superconducting material set forth in claim 1 wherein the atomic ratio of C ato Ba is selected in a range between 1% and 50%.
- The superconducting material set forth in claim 1 or 2 wherein said superconducting material has perovskite type or quasi-perovskite type crystal structure.
- The superconducting material set forth in any one of claim 1 to 3 wherein said superconducting material is in a form of bulk.
- The superconducting material set forth in any one of claim 1 to 3 wherein said superconducting material is in a form of paste with binder.
- The superconducting material set forth in any one of claim 1 to 3 wherein said superconducting material is in a form of a thin film.
- The process for producing a superconducting material, comprising preparing a material powder, compacting said material powder and then subjecting the resulting compact to final sintering, characterized in that said material powder is a member selected from a group consisting of:(A) a powder mixture composed of powders selected from a group comprising(i) powders of elements Ba, Cu, α, Dy, Ca and Tl and(ii) powders of compounds each containing at least one of said elements Ba, Cu, α, Dy, Ca and Tl,(B) a sintered powder obtained by sintering preliminarily the powder mixture (A) and then pulverizing a sintered mass and(C) a powder mixture of said powder mixture (A) and said sintered powder (B),in which, "α" represents Y or La,
wherein, an atomic ratio of (Ba, Ca) : (α, Dy) : Tl : Cu in said material powder satisfies a ratio of x : (1-x) : y : (1-y), in which an atomic ratio of Ca to Ba is selected in a range between 1 % and 90 %, an atomic ratio of Dy to α is selected in a range between 1 % and 90 %, x and y are numbers each satisfies ranges of 0 < x < 1 and 0 < y < 1 respectively. - The process set forth in claim 7 wherein the atomic ratio of Ca to Ba is selected in a range between 1 % and 50 %.
- The process set forth in claim 7 or 8 wherein said sintered powder (B) is obtained by repeating a series of preliminary sintering of the powder mixture (A) followed by pulverization for at least more than two times.
- The process set forth in any one of claim 7 to 9 wherein said compound or compounds are oxide, carbonate, sulfate, nitrate or oxalate each containing at least one of said elements of Ba, Cu, α, Dy, Ca and Tl.
- The process set forth in any one of claim 7 to 10 wherein said compound or compounds are in a form of powder having an average particle size of less than 10 µm.
- The process set forth in any one of Claim 7 to 11 wherein the final sintering is carried out at a temperature which is higher than 700 °C but is not higher than the lowest melting point of any one of compounds for a duration of from 1 to 50 hours.
- The process set forth in any one of claim 7 to 12 wherein said preliminary sintering is carried out in an atmosphere containing oxygen gas of 0.135 to 135 · 10² Pa (10⁻³ to 10² Torr).
- The process set forth in claim 7 or 13 wherein, after the final sintering complete, the resulting sintered mass is cooled at a cooling rate which is not slower than 1 °C/min but not higher than 1,000 °C/min.
- The process set forth in claim 7 or 14 wherein, after the final sintering complete, the resulting sintered mass is heat-treated at a temperature between 500 and 800 °C.
- The process set forth in claim 15 wherein said heat-treatment is carried out in an atmosphere containing oxygen gas of a partial pressure ranging from 0.135 to 135 · 10² Pa (10⁻³ to 10² Torr).
- The process set forth in any one of claim 7 to 15 wherein said superconducting material is used as a vapor source to prepare a thin film thereof on a substrate by physical vapor deposition technique.
- The process set forth in claim 17 wherein a deposited thin film is heat-treated at a temperature between 500 and 900 °C.
- The process set forth in claim 17 or 18 wherein the heat-treatment is carried out in oxygen containing atmosphere.
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP185739/87 | 1987-07-25 | ||
JP18573987 | 1987-07-25 | ||
JP185710/87 | 1987-07-26 | ||
JP18571087 | 1987-07-26 |
Publications (3)
Publication Number | Publication Date |
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EP0301952A2 EP0301952A2 (en) | 1989-02-01 |
EP0301952A3 EP0301952A3 (en) | 1990-02-07 |
EP0301952B1 true EP0301952B1 (en) | 1994-12-14 |
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EP88401931A Expired - Lifetime EP0301952B1 (en) | 1987-07-25 | 1988-07-25 | Compound oxide superconducting material and method for preparing the same |
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US (3) | US4880773A (en) |
EP (1) | EP0301952B1 (en) |
DE (1) | DE3852440T2 (en) |
Families Citing this family (26)
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US6559103B1 (en) | 1988-02-12 | 2003-05-06 | The Boeing Company | Method for producing superconducting oxide compounds |
US5175140A (en) * | 1987-03-19 | 1992-12-29 | Sumitomo Electric Industries, Ltd. | High Tc superconducting material |
JP2571789B2 (en) * | 1987-07-26 | 1997-01-16 | 住友電気工業株式会社 | Superconducting material and its manufacturing method |
JPH01252532A (en) * | 1987-11-11 | 1989-10-09 | Hitachi Ltd | Oxide superconductor |
US4962083A (en) * | 1988-02-12 | 1990-10-09 | University Of Arkansas | High temperature T1-Ba-Ca-Cu-O and T1-Sr-Cu-O superconductor |
US4994432A (en) * | 1988-01-15 | 1991-02-19 | University Of Arkansas | High temperature superconductor system and processes for making same |
US5106830A (en) * | 1988-01-15 | 1992-04-21 | University Of Arkansas | High temperature superconductor system having the formula Tl-Ba-Cu-O |
US5073536A (en) * | 1988-02-12 | 1991-12-17 | The University Of Arkansas | High temperature superconductors comprising Tl--Ca--Ba--O, Tl--Sr--Ba--Cu--O--Sr--Cu--O |
US5145834A (en) * | 1988-02-12 | 1992-09-08 | University Of Arkansas | Processes for making Tl-Ca-Ba-Cu-O, Tl-Sr-Ba-Cu-O and Tl-Sr-Cu-O superconductors by solid state synthesis |
US5112800A (en) * | 1988-08-25 | 1992-05-12 | The University Of Arkansas | Preparation of superconducting Tl-Ba-Ca-Cu-O thin films by Tl2 O3 |
EP0362685B1 (en) * | 1988-09-28 | 1993-02-10 | Nec Corporation | An oxide superconductor composition and a process for the production thereof |
US5036044A (en) * | 1988-09-29 | 1991-07-30 | University Of Arkansas | R-Tl-Sr-Ca-Cu-O superconductors |
US5389603A (en) * | 1988-10-25 | 1995-02-14 | At&T Corp. | Oxide superconductors, and devices and systems comprising such a superconductor |
DE68921144T2 (en) * | 1988-11-07 | 1995-06-14 | Nippon Electric Co | Oxide superconductor composition and process for its manufacture. |
US5356868A (en) * | 1989-07-03 | 1994-10-18 | Gte Laboratories Incorporated | Highly oriented superconductor oxide ceramic platelets and process for the production thereof |
US5120704A (en) * | 1989-11-08 | 1992-06-09 | The United States Of America As Represented By The Secretary Of The Navy | Method of making Tl-Sr-Ca-Cu-oxide superconductors comprising heating at elevated pressures in a sealed container |
EP0443827B1 (en) * | 1990-02-21 | 1996-07-17 | Her Majesty The Queen In Right Of New Zealand | Rare earth substituted thallium-based superconductors |
US5215962A (en) * | 1990-02-26 | 1993-06-01 | The University Of Arkansas | 90 K Tl-Ba-Ce-Cu-O superconductor and processes for making same |
US5096881A (en) * | 1990-03-15 | 1992-03-17 | The University Of Arkansas | Preparation of a superconducting Tl2 Ca2 Ba2 Cu3 O.sub.x2 O3 vapor |
US5407618A (en) * | 1990-08-13 | 1995-04-18 | The Boeing Company | Method for producing ceramic oxide compounds |
CA2043894A1 (en) * | 1990-09-12 | 1992-03-13 | Zhengzhi Sheng | M-r-t1-sr-cu-o based superconductors above liquid nitrogen temperature and processes for making same |
JP3205997B2 (en) * | 1990-09-21 | 2001-09-04 | 東レ株式会社 | Superconductor |
JPH04292815A (en) * | 1991-03-20 | 1992-10-16 | Sumitomo Electric Ind Ltd | Manufacture of bismuth-based oxide superconductor |
US5413987A (en) * | 1994-01-24 | 1995-05-09 | Midwest Research Institute | Preparation of superconductor precursor powders |
US6878420B2 (en) * | 2001-03-12 | 2005-04-12 | Lucent Technologies Inc. | MgB2 superconductors |
US6809042B2 (en) * | 2001-11-22 | 2004-10-26 | Dowa Mining Co., Ltd. | Oxide superconductor thick film and method for manufacturing the same |
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EP0284062A2 (en) * | 1987-03-24 | 1988-09-28 | Sumitomo Electric Industries Limited | Ceramic oxide superconductive composite material |
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FR2616012B1 (en) * | 1987-05-25 | 1991-03-29 | Centre Nat Rech Scient | METHOD FOR OPTIMIZING THE SUPERCONDUCTIVE PROPERTIES OF BA2YCU307-D COMPOUNDS |
US4962083A (en) * | 1988-02-12 | 1990-10-09 | University Of Arkansas | High temperature T1-Ba-Ca-Cu-O and T1-Sr-Cu-O superconductor |
US4870052A (en) * | 1988-03-08 | 1989-09-26 | International Business Machines Corporation | Tl-Ca-Ba-Cu-O compositions electrically superconducting above 120 degree K and processes for their preparation |
-
1988
- 1988-07-25 DE DE3852440T patent/DE3852440T2/en not_active Expired - Fee Related
- 1988-07-25 EP EP88401931A patent/EP0301952B1/en not_active Expired - Lifetime
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EP0284062A2 (en) * | 1987-03-24 | 1988-09-28 | Sumitomo Electric Industries Limited | Ceramic oxide superconductive composite material |
Non-Patent Citations (1)
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Physics Today, April 1988, pp. 21-25 * |
Also Published As
Publication number | Publication date |
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EP0301952A3 (en) | 1990-02-07 |
US4880773A (en) | 1989-11-14 |
DE3852440T2 (en) | 1995-07-27 |
US5093312A (en) | 1992-03-03 |
US5100866A (en) | 1992-03-31 |
DE3852440D1 (en) | 1995-01-26 |
EP0301952A2 (en) | 1989-02-01 |
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